1. Field of the Invention
This invention relates to a process for producing polymers of α-olefins, e.g., 1-hexene, 1-octene, 1-decene, 1-dodecene, and the like, in the presence of a metallocene catalyst, to form low molecular weight oligomers and polymers having viscosity and other physical properties suitable for synthetic lubricant applications.
2. Description of Related Art
Catalytic oligomerization of olefins is a known technique for manufacturing basestocks useful as lubricants. Efforts to improve upon the performance of natural mineral oil based lubricants by the synthesis of oligomeric hydrocarbon fluids have been the subject of important research and development in the petroleum industry for several decades, leading to recent commercial production of a number of superior poly(α-olefin) synthetic lubricants (hereinafter referred to as “PAO”). These materials are primarily based on the oligomerization of α-olefins, such as C2–C20 olefins. Industrial research effort on synthetic lubricants has generally focused on fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index (VI), while also showing lubricity, thermal, and oxidative stability and pour point equal to or better than mineral oil. These newer synthetic lubricants provide lower friction and hence increase mechanical efficiency across the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants.
Well known structural and physical property relationships for high polymers as contained in the various disciplines of polymer chemistry have pointed the way to α-olefins as a fruitful field of investigation for the synthesis of oligomers with the structure thought to be needed to confer improved lubricant properties thereon. Owing largely to studies on the polymerization of propene and vinyl monomers, the mechanism of the polymerization of α-olefins and the effect of that mechanism on polymer structure is reasonably well understood, providing a strong resource for targeting on potentially useful oligomerization methods and oligomer structures.
A significant problem in the manufacture of synthetic lubricants is the production of lubricants in a preferred viscosity range in good yield without excessive catalyst deactivation. Frequently, it is difficult to directly produce lower viscosity range lubes without incurring lower yields due to the production of non-lubricant range materials. Methods to control molecular weight of lubricants in the oligomerization step are sought after in the art to overcome the problems in the manufacture of, particularly, lower viscosity lubricants.
U.S. Pat. No. 4,769,510 discloses that in the polymerization of propylene and higher 1-olefins, polymers that have a high degree of isotacticity and a narrow distribution of molecular weight are obtained in the presence of a catalyst system composed of a zirconium compound that is stereo-rigid and chiral and a linear or cyclic aluminoxane. The catalyst system is said to be exceptionally active.
U.S. Pat. No. 5,145,819 discloses certain 2-substituted bisindenylmetallocenes that are said to form, together with aluminoxanes as cocatalysts, a very effective catalyst system for the preparation of polyolefins of high molecular weight.
U.S. Pat. No. 5,455,365 discloses a process for the preparation of an olefin polymer using metallocenes containing specifically substituted indenyl ligands. It is said that a highly effective catalyst system for the polymerization of olefins comprises a cocatalyst, preferably an aluminoxane, and a metallocene of a given structural formula.
U.S. Pat. Nos. 5,504,232 and 5,763,542 disclose a catalyst system for the polymerization of olefins that comprises a cocatalyst, preferably an aluminoxane, and a metallocene that contains specifically substituted indenyl ligands.
U.S. Pat. No. 5,672,668 discloses a process for the preparation of an olefin polymer by polymerization or copolymerization of an olefin of the formula Ra—CH═CH—Rb, in which Ra and Rb are identical or different and are a hydrogen atom or a hydrocarbon radical having 1 to 14 carbon atoms, or Raand Rb, together with the atoms connecting them, can form a ring, at a temperature of from −60° to 200° C., at a pressure of from 0.5 to 100 bar, in solution, in suspension or in the gas phase, in the presence of a catalyst formed from a metallocene of a given structural formula in the meso-form or a meso:rac mixture, with meso:rac>1:99, as transition-metal compound and a cocatalyst.
U.S. Pat. No. 5,688,887 discloses catalysts and processes to make low molecular weight, essentially terminally-unsaturated, viscous poly(1-olefin) or copoly(1-olefin) having a high terminal vinylidine content from a feed stock containing one or more 1-olefin and other volatile hydrocarbon liquids using a Ziegler catalyst made from a Group IVb metallocene and an aluminoxane cocatalyst, particularly bis(cyclopentadienyl) and bis(indenyl) titanium(IV), zirconium(IV) or hafnium(IV) compounds and methylaluminoxane. A particularly useful feedstock is said to be a refinery stream containing 1-olefins and isobutylene, which is used to make polyisobutylene. The reactive, essentially terminally-unsaturated, viscous poly(1-olefin) or copoly(1-olefin) can be functionalized to make a number of products useful as sealants, petroleum additives, adhesives, and the like by reacting the terminal vinylidine linkage with an aromatic, an epoxidation agent, a silylation agent, maleic anhydride, carbon monoxide and hydrogen, hydrogen, a halogen, a hydrohalogen, and the like.
U.S. Pat. No. 5,929,185 discloses copolymers that have a viscosity index VI of more than 160 and comprise A) from 99.0 to 99.99% by weight of C2–C20-alk-1-enes and B) from 0.01 to 1.0% by weight of C5–C20-α,ω-dienes having isolated double bonds.
U.S. Pat. No. 6,043,401 discloses catalysts and processes to make low molecular weight, essentially terminally-unsaturated, viscous poly(1-olefin) or copoly(1-olefin) having a high terminal vinylidine content from a feed stock containing one or more 1-olefin and other volatile hydrocarbon liquids using a Ziegler catalyst made from a Group IVb metallocene and an aluminoxane cocatalyst, particularly bis(cyclopentadienyl) and bis(indenyl) titanium(IV), zirconium(IV) or hafnium(IV) compounds and methylaluminoxane. A particularly useful feedstock is said to be a refinery stream containing 1-olefins and isobutylene, which is used to make polyisobutylene. The reactive, essentially terminally-unsaturated, viscous poly(1-olefin) or copoly(1-olefin) can be functionalized to make a number of products said to be useful as sealants, petroleum additives, adhesives, and the like by reacting the terminal vinylidine linkage with an aromatic, an epoxidation agent, a silylation agent, maleic anhydride, carbon monoxide and hydrogen, hydrogen, a halogen, a hydrohalogen, and the like.
U.S. Published Appl. No. 20020010290 discloses a process for producing a polymer of an α-olefin which comprises polymerizing an α-olefin having at least 4 carbon atoms in the presence of a catalyst for producing polymers of olefins which comprises (A) a specific metal compound and (B) at least one compound selected from (b-1) an organoaluminum oxy compound and (b-2) an ionic compound. The polymer of an α-olefin is said to be useful as a component of lubricant.
U.S. patent application Ser. No. 09/637,791, filed Aug. 11, 2000, describes a process for polymerizing 1-olefins to PAO with substantial saturation suitable for lubricant applications without need for further hydrogenation via the use of hydrogen with bridged cyclopentadienyl-fluorenyl metallocenes.
U.S. patent application Ser. No. 10/014911, filed Dec. 14, 2001, describes a process for copolymerizing 1-olefins and 2-norbomene to PAO with substantial saturation suitable for lubricant applications without need for further hydrogenation via the use of hydrogen with bridged cyclopentadienyl-fluorenyl metallocenes.
EP 0 613 873 A2 discloses a process for the preparation of liquid organic compounds, suitable as base materials for lubricants, comprising contacting one or more alpha-olefins containing 8 to 20 carbon atoms per molecule, under oligomerization conditions with a catalyst composition based on
a) a Group IV metal compound of the general formula (Cp)2MeX2, wherein Cp represents a cyclopentadienyl group, Me represents a Group IV A metal and each X independently represents a moiety selected from the group consisting of hydrocarbyl groups, hydrocarboxy groups, hydrocarbamido groups, each of which may be optionally substituted, hydrogen atoms and halogen atoms and
b) a substantially non-coordinating anion source;
and optionally subjecting the oligomers formed to an addition reaction to reduce their olefinic unsaturation.
WO 96/23751 discloses a process for preparing olefin oligomers with a molecular weight distribution Mw/Mn in a range from 1.0 to 2.4 by oligomerization of olefins in the presence of metallocene catalyst systems. The turbidity index of the catalyst-containing reaction mixture lies in a range from 1 to 10. The olefin oligomers are said to be useful as starting materials for preparing lubricants, fuel and oil additives, and as macromonomers.
WO 98/52888 discloses a process for the production of oligomers from an olefinic hydrocarbon feedstock. The process comprises oligomerizing olefins in the feedstock by means of a metallocene, catalyzed oligomerization reaction. The feedstock used is a Fisher-Tropsch-derived olefinic hydrocarbon feedstock comprising at most 65%, and typically 20–65%, by mass of α-olefins. In particular, the feedstock may comprise 30–50% by mass α-olefins, at most 30% by mass paraffins, at most 5% by mass oxygenated hydrocarbons and at most 5% by mass aromatic hydrocarbons.
WO 00/08066 discloses a catalyst system said to be suitable for preparing substantially terminally unsaturated a tactic polymers or copolymers of α-olefins having a number average molecular weight in the range 300–500,000 that comprises (A) a metallocene complex and (B) a cocatalyst comprising (i) a Group III Metal alkyl compound and (ii) a triaryl boron compound. Preferred metallocenes are those having alkyl ligands on the metal atom. The preferred Group III metal alkyl compound is triisobutyl aluminum and the preferred triaryl boron compound is tris(pentafluorophenyl)boron.
WO 00/08070 discloses a catalyst system said to be suitable for preparing substantially terminally unsaturated a tactic polymers or copolymers of α-olefins having a number average molecular weight in the range 300–500,000 comprises: A) a metallocene complex; and B) a cocatalyst comprising: i) an aluminoxane; and ii) a Group III metal alkyl compound having at least 2 carbon atoms. The use of the Group III metal compound allows for a reduction in the aluminoxane content in the cocatalyst. Preferred metallocenes are those having alkyl substitution on the cyclopentadienyl rings and the preferred Group III metal alkyl compound is triisobutyl aluminum.
Ewen, J., J. Am. Chem. Soc., 106:6355–6364 (1984), provides the first report of the use of a bridged, bis-indenyl metallocene for olefin polymerization, using Et(Ind)2TCl2. Propene polymerization of a rac/meso mixture of catalyst produces polypropylene identified with both isotactic and a tactic polymer in proportion to the rac/meso ratio. It is demonstrated that the meso form of the catalyst makes an a tactic polymer.
Herrmann, W., et al., Angew. Chem. Int. Ed. Engl., 28:1511–1512 (1989), provide the first open literature report of a silyl-bridged, bis-indenyl zirconocene. The authors report the separation and removal of the meso isomer is necessary because it otherwise leads to an “undesirable” a tactic polymer. The metallocene reported is unsubstituted, i.e., Me2Si(Ind)2ZrCl2.
Spaleck, W., et al., New J. Chem., 14:499–503 (1990), report a study of 14 different bridged metallocenes in propylene polymerization, mostly based on variations of the silyl-bridged, bis-indenyl zirconocene system. This paper is notable owing to the number of structural variations possible, but all studies are with rac isomers. Footnote 10 states that the meso-isomers were separated off.
Collins, S., et al., Organometallics, 10:2061–2068 (1991), report a study of rac and meso Et(Ind)2ZrCl2 and meso Et(IndH4)2ZrCl2 for polypropylene tacticity. The paper states that the polymerization activity is lower in the meso isomers, and produces a tactic polypropylene.
Pena, A, et al., Macromol. Rapid Commun., 12:353–358 (1991), report a study of 1-decene polymerization using traditional MgCl2-supported Ziegler-Natta catalyst systems, looking at the effects of Lewis base modification on degree of isotacticity. The paper is useful to confirm 13C-NMR assignments, DSC melt behavior, and to show that a number of systems, non-metallocene included, are capable of 1-decene polymerization.
Spaleck, W., et al., Angew. Chem. Int. Ed. Engl., 31:1347–1350, (1992), report the synthesis of and propene polymerization of by several substituted, silyl-bridged, bis-indenyl zirconocenes, including those bridged in the 2-indenyl and 2 and 4 positions. Substituted tetrahydroindenyl compounds are also reported. The rac isomer was used in all cases of polymerization reported.
Spaleck, W., et al., Macromol. Symp., 89:237–247 (1995), discuss structure-performance relationships in propene polymerization behavior with several modified silicon-bridged, bis-indenyl zirconocenes. Examples are provided of propene polymerizations with meso-isomers for the unsubstituted and 3-substituted silicon-bridged, bis-indenyl zirconocenes. All produce amorphous polymers, but molecular weight is increased with increasing substitution “bulk”.
Uozumi, T., et al., Macromol. Rapid Commun., 18:883–889 (1997), studied the copolymerization of ethylene and 1-octene with a meso-Me2Si(2-MeInd)2ZrCl2 catalyst system. Homopolymerizations of 1-octene were presented as part of the study, yielding a low molecular weight polymer that was identified as amorphous. Compared to the same results with rac-Me2Si(2-MeInd)2ZrCl2, the meso isomer was much less active in 1-octene homopolymerization.
Naga, N., et al., Macromol. Chem. Phys., 200:1587–1594 (1999), described the polymerization behavior of rac and meso isomers of —Me2Si(2-MeInd)2ZrCl2 with 1-propene, 1-butene, and 1-hexene to produce isotactic and a tactic homopolymers, respectively. The relative rates of polymerization between the two isomers are compared. It was concluded that for 1-hexene, coordination to the catalyst site is much more difficult for the meso-isomer than in propene or butene, resulting in a higher Rp(rac)/Rp(meso).
Resconi, L., in Metallocene-catalyzed polymers. Preparation Properties, and Technology; Kaminsky, W.; Scheirs, J., Eds.; Wiley, Vol. 1, pp. 467–484 (1999), provides a review of the synthesis and properties of a tactic polypropylene made using meso isomers and structurally aspecific metallocenes. The article states that, in general, the influence of hydrogen is to increase activity; however, in the work presented for a tactic polypropylene, hydrogen either has no effect or an adverse effect on activity. Also, hydrogen does not effect chain termination/chain transfer.
Schaverien, C., et al., Organometallics, 20:3436–3452 (2001), report the synthesis and polymerization activity of ethylene-bridged bis(2-indenyl) zirconocenes, both in the rac and meso forms. The paper demonstrates that the bridge does not necessarily have to be in the 1-position. Substituted indenyls are also made and used, i.e., 1-methyl-2-indenyl and 1-methyl-4-phenyl-2-indenyl rings bridged by ethylene. Polymers were made from ethylene, propylene, hexane, and copolymers of the three. The influence of hydrogen was also discussed.
Brüll, R, et al., Macromol. Symp., 165:11–18 (2001), report the polymerization of 1-pentene with a variety of bridged and unbridged metallocenes, forming oligomers and polymers ranging from dimers of pentene to molecular weights of 149,000. The paper demonstrates that the degree of polymerization is highly dependent on the metallocene catalyst. Also, a range of 1-olefins was studied from 1-pentene to 1-octadecene to demonstrate that the molar mass of the polyolefin decreases with increasing temperature. Molar mass is independent of chain length.
Grumel, V., et al., Macromol. Mater. Eng., 286:480–487 (2001), polymerized 1-olefins from pentene to octadecene with Cp2HfCl2, Me2C(Cp-9-Flu)ZrCl2, and rac-Et(Ind)2ZrCl2. The paper concludes that the molecular weight of the polymer is highly dependent on the catalyst, but is independent of monomer chain length. Also, there is a decrease in stereoregularity of the poly(1-olefin) with increasing monomer chain length for the stereospecific metallocenes used.
The disclosures of the foregoing are incorporated herein by reference in their entirety.